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Vol.4 No.1 previous AA39 - 40-SP6 ( 41 - 42 - 43 - 44 ) - NT 46 - 47
Academic Articles
Vol.4, No.2(2012) p.63 - p.103

Special Issue 6

Understanding and Managing Pipe Wall Thinning

Relevant Field
[Nuclear and Fossil Power Plant, Chemical Plant, Plant Life Management]
Nuclear Power Plant, Pipe Wall Thinning, Flow Accelerated Corrosion, Liquid Droplet Impingement, Nondestructive Inspection
Pipe wall thinning due to flow is a classic problem and this degradation has been basically well managed based on field data and experiences accumulated in plant maintenance activities. However, the thinning mechanisms, Flow Accelerated Corrosion (FAC) and Liquid Droplet Impingement (LDI), are not yet fully understood. Mechanistic investigation on FAC and LDI and development of powerful inspection tools are the keys to further improve management strategy of pipe wall thinning. In this special issue, key papers for understanding the characteristics and mechanisms of FAC and LDI and for developing novel inspection technologies have been invited.

Guest Editor,

Guest Editor,
Tetsuya Uchimoto


In a mechanistic model of flow-accelerated corrosion (FAC), one of the steps affecting the FAC rate is the mass transfer of ferrous ions from the oxide-water interface to the bulk of the flowing water. This step is dominant under alkaline conditions and high temperature, an environment frequently occurring in piping of nuclear power plants (NPPs). When the flow effects are dominant, the FAC rate is proportional to the mass flux of ferrous ions, which is typically proportional to the mass transfer coefficient in the flowing water. The mass transfer coefficient describes the intensity of the transport of corrosion products (ferrous ions) from the oxide-water interface into the bulk water. Therefore, this parameter can be used for predicting the local distribution of the FAC rate. The current paper presents a brief review of plant and laboratory evidence of the relationship between local mass transfer conditions and the FAC rate with examples for bends. It reviews the most important flow parameters affecting the mass transfer coefficient and, as an example, shows correlations for mass transfer coefficients in bends under NPP conditions. The role of geometry, surface roughness, wall shear stress, upstream turbulence, and locally generated turbulence is discussed. An example of computational fluid dynamics calculations and plant artefact measurements for short-radius and long-radius bends are presented.validity of the model is demonstrated by experiments using an angle beam transducer and a steel block with a side-drilled hole.


In this paper, the experiments on the wall thinning rate by the liquid droplet impingement in literature are studied by examining the erosion process, the method of erosion tests and the measurement accuracy of droplet velocity. Although the wall thinning rates scatter among the researchers, they come to a consistent result when the experimental conditions are considered. The power index of droplet velocity in the wall thinning rate ranges from 6 to 8 for the water jet and spray tests, while that of the rotating disk test shows smaller power index 5.8, which is closer to the theoretical value 5. The difference in the power indices is expected to be due to the influence of liquid film over the test specimen.

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Ryo MORITA, Fumio INADA, Michiya SAKAI, Shin-ichi MATSUURA, Shigenobu ONISHI and Mitsuo KUGIMOTO

For more realistic seismic safety evaluation of elbow with local thinning shape due to liquid droplet impingement erosion (LDI), a determination method of the thinning shape of the elbow due to LDI was developed, and a representative thinning shape for seismic evaluation of eroded elbows was proposed in this study. For the mechanistically-based determination of the thinning shape due to LDI, calculations of the droplet behavior and the thinning rate of the elbow were conducted. In addition, with this approach, the thinning shapes in various flow and piping size conditions were evaluated, and the enveloping thinning shape of those thinning shapes with a safety factor is considered as a representative thinning shape for seismic evaluation of eroded elbows.

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Gábor VÉRTESY, Ivan TOMÁŠ, Tetsuya UCHIMOTO and Toshiyuki TAKAGI

A recently developed nondestructive method, called Magnetic Adaptive Testing, which is based on systematic measurement and evaluation of minor magnetic hysteresis loops was applied for detection of local wall thinning in carbon steel, ferromagnetic T-shape tubes. Presently no effective inspection method is available for detection of wall thinning of a T-tube with reinforcing plate. It was shown that an artificially made slot can be reliable detected with good signal/noise ratio from the other side of the specimen even through the support plate.

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EJAM Vol.2 p.63-104 Academic Articles Special Issue on "Understanding and Managing Pipe Wall Thinning"